Alkaline lubricating oil



United States Patent 3,367,859 ALKALINE LUBRICATING OIL Howard BernardSilver, Esher, Surrey, and Alan Charles Dennison, Twickeuham, England,assignors to The British Petroleum Company Limited, London, England, acorporation of Great Britain No Drawing. Filed June 2, 1966, Ser. No.554,700 Claims priority, application Great Britain, June 18, 1965,25,847/ 65 '7 Claims. (Cl. 252-35) This invention relates to an alkalinelubricating oil that is capable of being water washed without seriousloss of alkalinity, and to the preparation of additives for such oils.

In recent years there has been a big increase in the use of residualfuels for the operation of certain types of internal combustion engines,particularly slow-speed diesel engines, such as are commonly used todrive ships. The use of these fuels is attractive owing to their lowcost compared with distillate fuels but it has been found that their usegives rise to certain problems one of which is an increase in crankcaseoil acidity which influences crankshaft corrosion. This trouble isbelieved to be due to the presence in residual fuels of certainmaterials, particularly those containing sulphur, which form acidicproducts on combustion, some of which acidic products find their wayinto the crankcase oil.

During the operation of slow-speed marine diesel engines it is customaryto circulate used crankcase oil from the pump through a filter andcooler and to subject a proportion of the circulating oil to a cleansingoperation. The cleansing operation comprises a water-Wash which has theeffect of coagulating insoluble materials (e.g., carbon) which are thenmore easily removed by subsequent centrifuging. It is customary to relyon this washing operation to reduce mineral acidity in the oil but thisis not always very satisfactory.

Another approach to the problem of oil acidity is to incorporate analkaline-reacting additive in the oil but, generally speaking, theadditives that have been found to give adequate neutralisation of acidsfrom cylinder drainings, tend to suffer from the drawback that they aretoo readily extracted from the oil by the Water Washing operationreferred to above. Examples of such additives are certain amines andcertain overbased calcium phenates and sulphonates.

In most large marine diesel engines the crankcase oil is also used forpiston cooling where it may be subjected to piston temperatures in theregion of 180 to 200 C. On many ships the same oil is also used for thetotal lubrication of auxiliary trunk-piston medium speed diesel engines.For both these applications an improvement in oxidation stability wouldbe an advantage.

We have now found a particular type of compound which is etfective inreducing the problem of lubricating oil acidity in slow-speed enginesand which is not readily removed from the oil by water washing. Inaddition the additives impart improved oxidation stability tolubricating oil base stocks rendering them more suitable for use in bothtypes of diesel engine.

According to the invention, there is provided a lubricating compositioncomprising a lubricating base oil, which may be mineral or synthetic,having blended therein from 0.01 to 20% wt., preferably 0.l-5% wt., ofthe composition, of a compound having the empirical formula (RCOO) Zn Owhere R is an alkyl, cycloalkyl, aryl, aralkyl or alkaryl grouppreferably having not more than 24 carbon atoms, the compound having atetrahedral structure with the four zinc atoms at the corners, theoxygen atom in the centre and the six carboxylate groups arranged alongthe sides. Most suitably R is an alkyl group having up to 18 carbonatoms.

ice

Compounds of this type may be prepared, according to another aspect ofthe invention, by reacting one molar proportion of zinc oxide with oneand a half molar proportions of an acid of the formula RCOOH, where R isas specified above, and removing all of the water formed during thereaction. The reaction is preferably carried out by refluxing with anazeotroping agent such as benzene or toluene. Excess zinc oxide may beused in the reaction but if the water formed is removed this excess doesnot react and it has to be filtered off from the product.

The reaction may be represented as follows:

However the reaction is believed to proceed in two stages as follows:

The base oil used in the compositions according to the invention isusually a refined lubricating oil obtained from petroleum, e.g., onehaving a viscosity in the range 3-50 centistokes at 210 F. and aviscosity index in the range -110.

The amount of the additive should preferably be such as to give thecomposition a total base number of 0.05- 100, preferably 0.5100, mg.KOH/ g.

It is to be understood that the lubricating composition may contain morethan one of the zinc compounds and that more than one carboxylic acidmay be used in the preparation of the compounds with the result that agiven molecule of the product may contain more than one type ofcarboxylic group.

A number of examples of the preparation of the zinc compounds will nowbe given. In all cases the reaction was carried out by heating a mixtureof four moles of zinc oxide with six moles of carboxylic acid intoluene, re-

moving the water formed during the reaction and filtering the reactionproduct. The acids used in the preparation of the compounds are shown inTable 1 which also gives certain data on the products. The inspectiondata is in all cases consistent with the expected properties of thecompounds.

TABLE 1 Total Z Compound Acid used in preparation Base No. Percent n mg.wt. KOH/g.

2-ethy1 hexanolc 383. 1 22. 8 Versatie 9, 11* 325 19.1 3,5,5-trimethylhexanoic 363 21. 4 Oleie 203 11.8 Gyclohexyl carboxylic 432 23. 9n-Octauoic 378 22. 5 Z-ethyl hexauoic, 50% 463 27. 2

molar; Grotonic, 50% molar. H. 2-ethyl hexanoie, 50% 435 25. 9 1. 4555molar; Pivalle, 50% molar.

Versatic 9, 11 i s a. commercially available Cry-C11 branched tertiarycarboxylic acid.

As is seen from the foregoing table, the number of carbon atoms presentin the carboxylic acids employed in the reaction ranges from 4 carbonatoms, as represented by crotonic acid, up to 18 carbon atoms, asrepresented by oleic acid.

In a further example, six moles of versatic 9, ll acid were reacted witheight moles of zinc oxide (i.e., a molar excess). The reactants wererefluxed in toluene, the water being removed as it was formed. Thetheoretical amount of water appropriate to the amount of acid wasobtained. On filtering the reaction product, approximately half of thezinc oxide originally used was separated from a toluene solution ofbasic zinc versatate 9, 11. The [01- uene was evaporated from the basiczinc salt which was found to have a TBN of 322.5.

The TBN of all the compounds prepared according to the invention wasfound to be very close to the theoretical value calculated from theempirical formula given above.

A number of lubricating compositions according to the invention Wereprepared using Compounds A and B in refined petroleum base oils. Thecompositions are shown in Table 2 which gives percentages by Weight ofthe ingredients and also the 210 F. viscosity (centistokes) andviscosity index of the base oils.

Composition P had a total base number (TBN) of 2.0 mg. KOH/ g. It didnot form stable emulsions with Water and after two washings with 20%distilled water at 60 C. its TBN was 1.7 mg. KOH/ g. which is consideredto be very satisfactory.

Composition R had a TBN of 1.38. It was given a much more severe waterwash using ten times its volume of distilled water at 70 C. After oneWash the TBN was 1.14 and after two washes it was 0.96, i.e., 83% and70% respectively of the original TBN. A commercially availablewater-Washable oil for marine engines gave figures of 44% and 13% whensubjected to the same test.

An anti-wear test was carried out on compositions Q and S using the FourBall test with a 15 kg. applied load. The results given in Table 3indicate that the zinc compounds improve the anti-wear properties ofbase oils.

TABLE 3 Wear soar diameter after 30 minutes 45 minutes 60 minutes SAE 90base oil... 0. 70 0. 70 0.80 Composition Q-.. 0.46 0. 52 0. 52 Liquidparafiin. 0.59 0.72 0.81 Composition S 0. 34 0.46 0.56

being water-washed Without serious loss of alkalinity comprising a majoramount of a lubricating base oil and from 0.01 to 20% by weight of thecomposition of a compound having the empirical formula (RCOO) Zn O,where R is selected from the group consisting of alkyl, cycloalkyl,aryl, aralkyl and alkaryl groups having up to 24 carbon atoms, thecompound having a tetrahedral structure with the four zinc atoms at thecorners, the oxygen atom in the center and the six carboxylate groupsarranged along the sides.

2. A composition according to claim 1, in which the proportion of thesaid compound in the composition is from 0.1 to 5% wt.

3. A composition according to claim 1, in which the proportion of thesaid compound in the composition is" such that the composition has atotal base number of from 0.05 to mg. KOH/g.

4. A composition according to claim 1, in which the proportion of thesaid compound in the composition is such that the composition has atotal base number of from 0.5 to 100 mg. KOH/g.

5. A composition according to claim 1, in which R is an alkyl grouphaving 4 to 18 carbon atoms.

6. A method of preparing a compound suitable for use as a lubricatingoil additive and having the empirical formula (RCOO) Zn O, wherein R isselected from the group consisting of alkyl, cycloalkyl, aryl, aralkyland alkaryl groups having up to 24 carbon atoms which comprises reactingone molar proportion of zinc oxide with one and a half molar proportionsof an acid of the formula RCOOH, refluxing the reactants with anazeotroping agent, and removing all of the water formed during thereaction.

7. A method according to claim 6, in which R is an alkyl group having 4to 18 carbon atoms.

References Cited UNITED STATES PATENTS 1,767,076 6/1930 Jarman 252-352,362,233 11/1944 Bannon 25235 2,384,551 9/1945 Jehle 25235 2,501,1273/1950 Kebrich 260429 9 3,017,361 1/1962 Morris et al. 25235 FOREIGNPATENTS 891,858 3/1962 Great Britain.

OTHER REFERENCES Koyama et a1.: Crystal Structure Zinc Oxyacetate, inChemical Abstracts of J.A.C.S., vol 49 (1955), page 12909h.

DANIEL E. WYMAN, Primary Examiner.

C. F. DEES, Assistant Examiner.

1. AN ALKALINE LUBRICATING OIL COMPOSITION CAPABLE OF BEING WATER-WASHEDWITHOUT SERIOUS LOSS OF ALKALINITY COMPRISING A MAJOR AMOUNT OF ALUBRICATING BASE OIL AND FROM 0.01 TO 20% BY WEIGHT OF THE COMPOSITIONOF A COMPOUND HAVING THE EMPIRICAL FORMULA (RCOO)6ZN4O, WHERE R ISSELECTED FROM THE GROUP CONSISTING OF ALKYL, CYCLOALKYL, ARYL, ARALKYLAND ALKARYL GROUPS HAVING UP TO 24 CARBON ATOMS, THE COMPOUND HAVING ATETRAHEDRAL STRUCTURE WITH THE FOUR ZINC ATOMS AT THE CORNERS, THEOXYGEN ATOM IN THE CENTER AND THE SIX CARBOXYLATE GROUPS ARRANGED ALONGTHE SIDES.
 6. A METHOD OF PREPARING A COMPOUND SUITABLE FOR USE AS ALUBRICATING OIL ADDITIVE AND HAVING THE EMPIRICAL FORMULA (RCOO)6ZN4O,WHEREIN R IS SELECTED FROM THE GROUP CONSISTING OF ALKYL, CYCLOALKYL,ARYL, ARALKYL AND ALKARYL GROUPS HAVING UP TO 24 CARBON ATOMS WHICHCOMPRISES REACTING ONE MOLAR PROPORTION OF ZINC OXIDE WITH ONE AND AHALF MOLAR PROPORTIONS OF AN ACID OF THE FORMULA RCOOH, REFLUXING THEREACTANTS WITH AN AZEOTROPING AGENT, AND REMOVING ALL OF THE WATERFORMED DURING THE REACTION.